The invention concerns a device for the removal of condensate from a steam-heated drying cylinder, specifically for a paper machine. A condensate suction tube rotating with the drying cylinder extends from the area of the axis of rotation of the drying cylinder toward the inside surface of the cylinder shell and has a suction opening for picking up condensate mixed with steam. A steam blowing line originating from the cylinder interior and featuring an annular channel empties in the area of the suction opening in the interior of the condensate suction pipe. Drying cylinders of this type preferably serve in paper machines for drying a newly formed paper web.
Experts call such a device for condensate removal briefly a "rotating siphon." This design has the advantage that no relative movement is taking place between the revolving drying cylinder and the condensate suction pipe, since the condensate suction pipe is rigidly fastened in the drying cylinder, with both then rotating jointly. Another known type of siphon design is the stationary siphon, which does not share the rotary movement of the drying cylinder.
In regular drying cylinders, such as that described in U.S. Pat. No. 4,718,177 the cylinder shell has a smooth inside wall, on which the condensate to be removed, at higher machine speed, is forming a ring. There is mostly only a single condensate suction pipe present, for instance with a bell or dish-shaped suction mouthpiece.
In the case of glazing or crepe cylinders, such as described in U.S. Pat. No. 4,359,829, the diameter of which amounts to 2 to 4 times that of a regular drying cylinder, the inside of the cylinder shell is provided with peripheral grooves in which the condensate to be removed is collected. Therefore, there is at least one condensate collection pipe provided which extends approximately parallel to the cylinder axis and rotates with the cylinder, and to which numerous radial siphon tubelets are connected which extend into the grooves. In this case, the condensate suction pipe protrudes into the interior of the condensate collection pipe so as to suck the condensate out.
The removal of the condensate is accomplished in all cases in that inside the drying cylinder a higher steam pressure is adjusted than in the condensate suction pipe (facultatively including the suction mouthpiece). Due to this "differential pressure," part of the supplied steam continuously exits outside through the rotating siphon, mixing with a certain amount of condensate and feeding it outside.
In regular drying cylinders it is also known to provide an additional steam blowing line that originates from the cylinder space and empties in the region of the suction opening of the condensate suction pipe. This makes is possible to exert an increased transport effect on the condensate. Specifically, it is possible to ensure with the aid of such an additional steam blowing line that the removal of the condensate will also be assured (or restarted), when too much condensate has accumulated as a result of any disturbance or in the case of a temporary standstill of the drying cylinder. In this case, the suction opening of the condensate suction pipe may at least temporarily be flooded by the condensate, causing the normal condensate transport to be disrupted; i.e., the condensate removal is temporarily taking place only through that steam which through the additional steam blowing line is fed to the condensate suction pipe.
It is known to provide as an additional steam blowing line simply a bore extending through the wall of the condensate suction pipe (U.S. Pat. No. 2,993,282). However, such a bore must be arranged a relatively short distance from the suction opening of the condensate suction pipe, giving rise to the risk that now and then the bore will also be flooded.
Other prior designs avoid this disadvantage: according to the previously cited U.S. Pat. No. 4,718,177, the additional steam blowing line extends from the side into the interior of the suction mouthpiece and then along the inside surface of the cylinder shell and through the suction mouthpiece. Although with this prior design the desired effect is actually achievable, there is a desire for further improvement.
According to the German patent document 24 13 271, on which the invention is based, there is a steam blowing line provided which is arranged coaxially within the condensate suction pipe; it features inside the suction mouthpiece a reversing device that forms an annular channel. Thus, the additional steam is fed to the interior of the condensate suction pipe in such a way that it will be evenly distributed across the circumference of the condensate suction pipe. The objective with this known arrangement is to increase the transport effect of the additional steam on the condensate; however, this is not sufficiently accomplished because the installations required in the condensate suction pipe and in the suction mouthpiece cause relatively high flow resistances. In other words, the installations slow down the condensate flow, so that a relatively high differential pressure is needed, which results in a relatively high steam consumption. In addition, the installations are relatively expensive. Furthermore, it is very difficult or even entirely impossible to retroactively equip a present condensate suction pipe with the steam blowing line.
The problem underlying the invention is to design a condensate removal device featuring an additional steam blowing line so that the steam consumption caused by the additional steam blowing line, as compared with prior designs, will be reduced while nonetheless a maximally high transport effect is exerted on the condensate to be removed.